Electrically modulated transport of diclofenac salts through hydrogels of sodium alginate, carbopol, and their blend polymers

Smart and Intelligent Stimuli Responsive Materials: An Innovative Step in Drug Delivery System

Background:

In the field of drug delivery, smart and intelligent approaches have gained significant attention among researchers in order to improve the efficacy of conventional dosage forms. Material science has played a key role in developing these intelligent systems that can deliver therapeutic cargo on-demand. Stimuli responsive material based drug delivery systems have emerged as one of the most promising innovative tools for site-specific delivery. Several endogenous and exogenous stimuli have been exploited to devise “stimuli-responsive” materials for targeted drug delivery.

Methods:

For better understanding, these novel systems have been broadly classified into two categories: Internally Regulated Systems (pH, ionic strength, glucose, enzymes, and endogenous receptors) and Externally Regulated Systems (Light, magnetic field, electric field, ultrasound, and temperature). This review has followed a systematic approach through separately describing the design, development, and applications of each stimuli-responsive system in a constructive manner.

Results:

The development includes synthesis and characterization of each system, which has been discussed in a structured manner. From advantages to drawbacks, a detailed description has been included for each smart stimuli responsive material. For a complete review in this niche area of drug delivery, a wide range of therapeutic applications including recent advancement of these smart materials have been incorporated.

Conclusion:

From the current scenario to future development, a precise overview of each type of system has been discussed in this article. In summary, it is expected that researchers working in this novel area will be highly benefited from this scientific review.

Alginate Particles as Platform for Drug Delivery by the Oral Route: State-of-the-Art

Pharmaceutical research and development aims to design products with ensured safety, quality, and efficacy to treat disease. To make the process more rational, coherent, efficient, and cost-effective, the field of Pharmaceutical Materials Science has emerged as the systematic study of the physicochemical properties and behavior of materials of pharmaceutical interest in relation to product performance. The oral route is the most patient preferred for drug administration. The presence of a mucus layer that covers the entire gastrointestinal tract has been exploited to expand the use of the oral route by developing a mucoadhesive drug delivery system that showed a prolonged residence time. Alginic acid and sodium and potassium alginates have emerged as one of the most extensively explored mucoadhesive biomaterials owing to very good cytocompatibility and biocompatibility, biodegradation, sol-gel transition properties, and chemical versatility that make possible further modifications to tailor their properties. The present review overviews the most relevant applications of alginate microparticles and nanoparticles for drug administration by the oral route and discusses the perspectives of this biomaterial in the future.

From Drug Dosage Forms to Intelligent Drug-delivery Systems: a Change of Paradigm

The design of new drug-delivery systems (DDSs) able to regulate the moment and the rate at which the release should take place, and even to target the drug to specific tissues and cell compartments, has opened novel perspectives to improve the efficacy and safety of the therapeutic treatments. Ideally, the drug should only have access to its site of action and the release should follow the evolution of the disease or of certain biorhythms. The advances in the DDSs field are possible because of a better knowledge of the physiological functions and barriers to the drug access to the action site, but also due to the possibility of having “active” excipients that provide novel features. The joint work in a wide range of disciplines, comprising materials science, biomedical engineering and pharmaceutical technology, prompts the design and development of materials (lipids, polymers, hybrids) that can act as sensors of physiological parameters or external variables, and as actuators able to trigger or tune the release process. Such smart excipients lead to an advanced generation of DDSs designed as intelligent or stimuli-responsive. This chapter provides an overview of how the progress in DDSs is intimately linked to the evolution of the excipients, understood as a specific category of biomaterials. The phase transitions, the stimuli that can trigger them and the mechanisms behind the performance of the intelligent DDSs are analyzed as a whole, to serve as an introduction to the topics that are comprehensively discussed in the subsequent chapters of the book. A look to the future is also provided.

Novel pH- and temperature-responsive blend hydrogel microspheres of sodium alginate and PNIPAAm-g-GG for controlled release of isoniazid

This paper reports the preparation and characterization of novel pH- and thermo-responsive blend hydrogel microspheres of sodium alginate (NaAlg) and poly(N-isopropylacrylamide)(PNIPAAm)-grafted-guar gum (GG) i.e., PNIPAAm-g-GG by emulsion cross-linking method using glutaraldehyde (GA) as a cross-linker. Isoniazid (INZ) was chosen as the model antituberculosis drug to achieve encapsulation up to 62%. INZ has a plasma half-life of 1.5 h, whose release was extended up to 12 h. Fourier transform infrared spectroscopy was used to confirm the grafting reaction and chemical stability of INZ during the encapsulation. Differential scanning calorimetry was used to investigate the drug's physical state, while powder X-ray diffraction confirmed the molecular level dispersion of INZ in the matrix. Scanning electron microscopy confirmed varying surface morphologies of the drug-loaded microspheres. Temperature- and pH-responsive nature of the blend hydrogel microspheres were investigated by equilibrium swelling, and in vitro release experiments were performed in pH 1.2 and pH 7.4 buffer media at 37°C as well as at 25°C. Kinetics of INZ release was analyzed by Ritger-Peppas empirical equation to compute the diffusional exponent parameter (n), whose value ranged between 0.27 and 0.58, indicating the release of INZ follows a diffusion swelling controlled release mechanism.

Electroresponsive Polyacrylamide-grafted-xanthan Hydrogels for Drug Delivery

An electroresponsive drug delivery system was developed using poly(acrylamide-grafted-xanthan gum) (PAAm-g-XG) hydrogel for transdermal delivery of ketoprofen. The electrically sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under nitrogen atmosphere followed by alkaline hydrolysis. When a swollen PAAm-g-XG hydrogel was placed in between a pair of electrodes, deswelling of the hydrogel was observed in the vicinity of electrodes carrying the electric stimulus. The membrane-controlled drug delivery systems were prepared using drug-loaded PAAm-g-XG hydrogel as the reservoir and crosslinked with poly(vinyl alcohol) to form films as rate controlling membranes (RCM). The in vitro drug permeation study from the formulations was performed through excised rat abdominal skin. Drug permeation across the skin was greatly enhanced in the presence of electric stimulus as compared to passive diffusion and was found to be dependent upon the applied electric current strength and crosslink density of RCM. A pulsated pattern of drug release was observed as the electric stimulus was switched `on' and `off.' The skin histopathology study demonstrated that, after the application of an electrical stimulus, there were changes in the structure of stratum corneum and cell structure. These PAAm-g-XG hydrogel could be useful as transdermal drug delivery systems actuated by an electric signal to provide on-demand release of drugs.

Light-sensitive intelligent drug delivery systems

Drug delivery systems (DDS) capable of releasing an active molecule at the appropriate site and at a rate that adjusts in response to the progression of the disease or to certain functions/biorhythms of the organism are particularly appealing. Biocompatible materials sensitive to certain physiological variables or external physicochemical stimuli (intelligent materials) can be used for achieving this aim. Light-responsiveness is receiving increasing attention owing to the possibility of developing materials sensitive to innocuous electromagnetic radiation (mainly in the UV, visible and near-infrared range), which can be applied on demand at well delimited sites of the body. Some light-responsive DDS are of a single use (i.e. the light triggers an irreversible structural change that provokes the delivery of the entire dose) while others able to undergo reversible structural changes when cycles of light/dark are applied, behave as multi-switchable carriers (releasing the drug in a pulsatile manner). In this review, the mechanisms used to develop polymeric micelles, gels, liposomes and nanocomposites with light-sensitiveness are analyzed. Examples of the capability of some polymeric, lipidic and inorganic structures to regulate the release of small solutes and biomacromolecules are presented and the potential of light-sensitive carriers as functional components of intelligent DDS is discussed.

Polysaccharide hydrogels for modified release formulations

Hydrogels are three-dimensional, hydrophilic, polymeric networks, with chemical or physical cross-links, capable of imbibing large amounts of water or biological fluids. Among the numerous macromolecules that can be used for hydrogel formation, polysaccharides are extremely advantageous compared to synthetic polymers being widely present in living organisms and often being produced by recombinant DNA techniques. Coming from renewable sources, polysaccharides also have frequently economical advantages over synthetic polymers. Polysaccharides are usually non-toxic, biocompatible and show a number of peculiar physico-chemical properties that make them suitable for different applications in drug delivery systems. We review here a selection of the most important polysaccharides that have been studied and exploited in several fields related to pharmaceutics. Particular attention has been focused on the techniques used for the hydrogel network preparation, on the drug delivery results, on clinical applications as well as on the possible use of such systems as scaffolds for tissue engineering.

Drug delivery strategies using polysaccharidic gels

Hydrogels are hydrophilic polymeric networks, with chemical or physical crosslinks, that are capable of swell and can retain a large amount of water. Among the numerous types of macromolecules that can be used for hydrogel formation, polysaccharides show very attractive advantages in comparison to synthetic polymers. They are widely present in living organisms, are usually abundant and show a number of peculiar physicochemical properties; furthermore, these macromolecules are, in most cases, non-toxic, biocompatible and can be obtained from renewable sources. For these reasons, polysaccharides seem to be particularly suitable for different applications in the wide field of pharmaceutics. As examples of the studies that have been carried out on this topic, this review will focus on two polysaccharides, alginate and xyloglucan. Alginate has been, and still is, extensively investigated and has numerous industrial applications, whereas xyloglucan was chosen because, although it has been much less studied, it shows interesting properties that should find important practical uses in the near future. The possible advantages of physical gels over those that are chemically crosslinked are also discussed.